1. Field of the Invention
This invention relates to a process for the hydrodesulfurization of hydrocarbons with a fluorided platinum catalyst and more particularly to the use of an oxygen-containing hydrogenation moderator to lower the saturation of unsaturated hydrocarbons by the hydrodesulfurization process.
2. The Prior Art
Unleaded gasolines contain some sulfur, generally as organo-sulfur compounds, whose concentration varies with the source and prior processing of the gasolines. The catalytic treatment of the exhaust gases from internal combustion engines using sulfur-containing unleaded gasolines produces sulfur oxides. For various reasons it may be desirable to reduce the sulfur oxides emissions. One method of accomplishing this is by reducing the sulfur content of the unleaded gasolines.
The use of a cobalt-molybdenum catalyst on alumina, or the use of a nickel catalyst, to desulfurize gasoline is known in the art but is an expensive process. Such catalysts require high pressures and large quantities of generally expensive catalytic material. The use of high pressures requires special high pressure hydrogenation equipment which is itself expensive and is also expensive to operate.
The use of platinum as a catalyst for desulfurization was previously thought to be impossible due to the rapid deactivation of the platinum catalyst by sulfur and sulfur compounds. It recently has been found that a highly fluorided platinum catalyst retains some resistance to sulfur poisoning so that such a catalyst can be used for the desulfurization of a feedstock.
The fluorided platinum catalyst and the process for using it are disclosed in U.S. Pat. No. 3,435,085. In the disclosed process, hydrocarbons or other feedstocks are desulfurized by contacting the feedstock with hydrogen in the presence of the fluorided platinum. However, the fluorided platinum also catalyzes the hydrogenation of unsaturated hydrocarbons to saturated hydrocarbons. Such saturation is undesirable in unleaded gasolines since the saturation of multiple carbon bonds lowers the octane number of the gasolines. Gasolines of a higher octane number are more desirable in internal combustion engines because of their antiknock properties. Further, the hydrogenation process disclosed in U.S. Pat. No. 3,345,085 requries the use of hydrogen at very high pressures, such as 83 kilograms per square centimeter (1200 psia) and preferably between 69 and 277 kilograms per square centimeter (1000 to 4000 psia). Such pressures are costly to use because, for among other reasons, the equipment required for hydrogenation at such pressures is costly to build and maintain.
Fluorided platinum has been found to be useful in the selective hydrogenation of polycyclic aromatics, such as disclosed in U.S. Pat. No. 3,285,984. A low pressure, 6.9 to 34.6 kilograms per square centimeter, hydrogenation process using a fluorided platinum catalyst is disclosed in U.S. Pat. No. 2,757,128, however, it is disclosed that the saturation of olefins occurs.
Coassigned U.S. Pat. No. 3,711,566, discloses the low pressure hydrogenation of aromatic hydrocarbons in the presence of sulfur using a fluorided platinum catalyst. Very small quantities, in the order of about 2.5.times.10.sup.-5 to 1.0.times.10.sup.-3 gram mole of carbon monoxide per hour per gram of the fluorided platinum alumina catalyst as disclosed as being used to inhibit hydrocracking reactions.
Coassigned U.S. Pat. No. 3,711,399 discloses a process for the selective hydrocracking and isomerization of hydrocarbon feedstocks with hydrogen and a small quantity of carbon monoxide. The disclosed process converts paraffin hydrocarbons, having at least 6 and up to 40 carbon atoms to hydrocarbons having considerable branching. However, the process is only disclosed as being useful for paraffins which already are completely saturated.
Coassigned U.S. Pat. No. 3,756,941 discloses the dehydroisomerization of alkylcyclopentanes, gasoline and naphtha fractions into aromatic compounds by the use of a catalyst and a process similar to that disclosed in the two previously cited patents. Again a very small quantity of carbon monoxide is used, and it is used to reduce the cracking property of the fluorided platinum catalyst. No mention is made of preventing the saturation of unsaturated hydrocarbons and of desulfurization.
In coassigned U.S. Pat. Nos. 3,711,566; 3,711,399, and 3,756,941, cited above, it is disclosed that the beneficial effects provided by the carbon monoxide is unexpected in as much as carbon monoxide has long been considered a strong general poison to platinum metal catalysts. Further, the quantities of carbon monoxide disclosed as being useful are very small, being no greater than about 1.times.10.sup.-3 gram mole of carbon monoxide per hour per gram of fluorided platinum alumina catalyst. In all of the cited prior art there is no disclosure that the saturation of multiple carbon bonds is prevented or is reduced in any way by the presence of the carbon monoxide.